1. Field of the Invention:
The invention relates to electrodes and leads for conducting electrical signals to and from muscle tissue, and especially to electrodes and leads useful for intravenously conducting such signals to and from endocardial electrodes.
2. Description of the Prior Art:
In the past, various types of endocardial leads and electrodes thereof have been intravenously introduced into different chambers of a patient's heart, including the right ventricle, the atrium, the right atrial appendage, and the coronary sinus. A typical endocardial lead includes a sleeve composed of silicone rubber, which is resistent to deterioration caused by body fluids and does not cause adverse reaction by the patient's body. A helical coil embedded in the silicone rubber sleeve is electrically connected to a distal electrode which is introduced into the heart and a proximal electrode electrically connected to the opposite end of the helical coil conductor to allow electrical connection of the lead to electronic equipment, such as an electronic pacemaker. Typically, a stylet made of thin spring steel wire and having a handle at one end thereof is removeably inserted through the length of the helical coil conductor. Turning of the handle permits a physician to manipulate and control the distal end of the lead as it is intravenously introduced into the heart.
Both unipolar leads (including a single helical coil conductor embedded in a single, silicone rubber sleeve) and bipolar leads (including two helical conductors embedded in a single silicon rubber sleeve) have been utilized. Such intravenous leads are readily available from various manufacturers, including Cardiac Pacemakers, Inc., of St. Paul, Minn., Inter-Medics. Inc., of Freeport, Tex., and Med-Tronic, Inc., of Minneapolis, Minn.
Recently, surgeons have attempted to introduce several leads into the heart of a patient in order to accomplish atrioventricular (AV) sequential pacing, which has been made possible by recently developed AV sequential pulse generators. AV sequential pacing makes it possible for the heart of a patient to achieve maximum cardiac output by causing the upper and lower chambers of the heart to fire in optimum time sequence such that the receiving chamber can receive an optimum amount of blood, which can then be pumped in proper time sequence to the periphery of the body.
Ordinarily, the cephalic veins at the shoulder level or the internal or external jugular veins in the neck of a patient are surgically opened and endocardial leads are introduced through the respective venous openings. The desirability of inserting two endocardial leads to achieve AV sequential pacing has posed a problem to the surgeon, since two (rather than only one) incisions must be made in two veins which have continuity with the right side of the heart in order to pass two endocardial leads intravenously into the heart. The leads must be passed parallel to each other through the accessible veins. This situation can result in dislodgement of a first lead which has been initially inserted into a proper position in the heart. Further, when multiple leads are lodged in different portions of the heart, the leads sometimes rub against each other due to lead flexing caused by beating of the heart. The forces produced as a result of the rubbing sometimes cause dislodging of electrodes attached to the leads. There is presently an unmet need for a reliable system for introducing multiple endocardial leads intravenously into the heart without the surgical complexity that now exists.
Accordingly, it is an object of the invention to provide a system and method of intravenously introducing an endocardial lead into a patient's heart with minimum danger of dislodging an endocardial lead previously introduced and lodged within the patient's heart.
It is another object of the invention to provide a system and method of intravenously introducing an endocardial lead into a patient's heart without the requirement that individual leads be passed through separate incisions into one or more veins of the patient.
It is another object of the invention to provide an endocardial lead system which avoids rubbing between leads due to flexing of the leads caused by beating of the heart in which the leads are lodged.
It has been very difficult to introduce prior endocardial leads into the coronary sinus or to attain the J-shaped curvature necessary to attach an electrode to the right atrial appendage, as is desirable in some instances to attain AV sequential pacing. U.S. Pat. Nos. 3,865,118; 4,057,067; and 4,154,247 disclose endocardial leads designed to make atrial contact. The device disclosed in U.S. Pat. No. 3,865,118 includes a catheter of coaxial design. This device includes spring electrodes connected to both inner and outer conductors for contacting the apex of the ventricle and outer atrium, respectively. This device does not allow the controlling of the positions of the leads, except as to their depth, by the physician. Further, spring electrodes can be a source of clot formation. Further, due to the springing characteristic of electrodes, laceration or perforation of the vena cava can occur. Further, the disclosed device is incapable of contacting optimum muscle tissue locations in the heart to accomplish optimum AV sequential pacing. Further, repositioning of the distal spring electrodes after initial lodging in heart muscle tissue may be dangerous.
It is another object of the invention to provide a multiple lead endocardial lead assembly and method which enables a surgeon to independently control the depth of insertion of a second lead into a second heart chamber, after a first lead has been inserted into a first heart chamber.
It is another object of the invention to provide a multiple lead endocardial lead assembly which does not depend upon springiness of a lead to maintain electrode contact with muscle tissue of the heart.
It is another object of the invention to provide a multiple lead endocardial lead assembly which has no tendency to lacerate heart tissue as a result of continual beating of the heart for a very long period of time.
The device disclosed in U.S. Pat. No. 4,057,067 discloses a single bipolar lead structure having an atrial electrode structure which assumes a J-shaped configuration, enabling the atrial electrode to be hooked onto the atrial appendage at the time the ventricular component and the electrode thereon is firmly engaged against the right ventricular wall. During insertion, a stylet maintains the atrial component in a linear configuration. When the stylet is removed the atrial component springs into the desired J-shaped configuration. This device has the problem that the lengths of the ventricle and atrial tips cannot be adjusted for various sized hearts or anatomical configuration. Further, the ventricle tip can become dislodged when the atrial component is released by withdrawing the stylet. The device is not suitable for stimulating tissue in the coronary sinus.
It is another object of the invention to provide a multiple lead endocardial lead assembly which allows independent adjustment of the depth of one of the leads after another of the leads has been positioned in the heart, and is suitable for insertion of one lead into either the coronary sinus or the atrial appendage and is also suitable for insertion of another lead into the right ventricle.
The device disclosed in U.S. Pat. No. 4,154,247 discloses a bipolar lead including a sheath having an insulating layer which, when heated, by immersing it into boiling water, enables the lead to be formed into a particular configuration. When the lead cools, it "sets" into a new deformable configuration. The device has the shortcoming that it is a bipolar lead having two electrodes disposed along a single lead. It relys on its deformed configuration to maintain spring pressure of the electrode against suitable portions of the ventricle and atrium. This results in unreliable electrical contact to tissue in a beating heart. The device is not suitable for contacting muscle tissue both of the ventricle and the coronary sinus, and provides minimal capacity for manipulation of the electrodes by a physician.
Accordingly, another object of the invention is to provide a multiple lead endocardial assembly and method which overcomes the above shortcomings of prior endocardial leads.